Lipid-analogous phosphoric triesters

ABSTRACT

The present invention relates to novel phosphoric triesters which comprise apolar lipid structures.

CROSS-REFERENCE TO THE APPLICATION

The present application is a continuation of U.S. application Ser. No. 10/529,889, filed Apr. 1, 2005, which is a national stage filing under 35 U.S.C. §371 of PCT/EP2003/010870, filed Oct. 1, 2003, which in turn claims priority to DE 10245909.6, filed Oct. 1, 2002, all of which applications are hereby incorporated by reference in their entireties.

DESCRIPTION

The present invention relates to novel phosphoric triesters which comprise apolar lipid structures.

These triesters can be used in particular as liposome constituents.

One aspect of the invention is a compound of the formula (I)

in which R¹ is a residue selected from cholesterol, diacylglycerols, dialkylglycerols, acylalkylglycerols, ceramides, primary or secondary alcohols having 12 to 24 C atoms or acylglycerobenzyl ethers, R² is a residue selected from ethanolamine, N-methylethanolamine, propanolamine, choline, glycerol, oligoglycerols, glycoglycerols or serine, each of which may optionally comprise protective groups, and R³ is a radical selected from C₁-C₈-alkyl or C₁-C₈-alkenyl or has the meaning of R².

The compounds of the invention are lipid-analogous phosphoric triesters, in particular phosphoric triesters having multiple hydroxyl groups per phosphorus atom, in particular at least two hydroxyl groups per phosphorus atom, more preferably at least three hydroxyl groups per phosphorus atom and even more preferably at least four hydroxyl groups per phosphorus atom.

The phosphoric triesters of the invention comprise a residue R¹ which comprises an apolar lipid structure. Suitable structures for R¹ are in particular cholesterol residues, so that preferred phosphoric triesters are cholesteryl compounds.

A further preferred residue for R¹ is diacylglycerol, where the acyl groups each comprise independently preferably 12 to 28, in particular 13 to 27 and more preferably 14 to 26 carbon atoms. The acyl radicals may be saturated or mono- or poly-, in particular di- or triunsaturated radicals. Acylglycerols which comprise unsaturated fatty acid residues such as, for example, residues of oleic acid, linoleic acid or linolenic acid are particularly preferred.

The residue R¹ may additionally according to the invention be a dialkylglycerol residue, wherein the alkyl radicals each independently of one another preferably have 1 to 28, in particular 12 to 26, even more preferably 14 to 24 carbon atoms. The alkyl radicals in the dialkylglycerol residue may be saturated or mono- or poly-, in particular di- or triunsaturated. Preferred radicals are (Z)-9-octadecenyl-, (Z.Z.)-9.12-octadecanedienyl-, (Z.Z.Z)-9.12.15-octadecanetrienyl, and lipophilic basic structures with a pharmaceutical effect, such as 1-octadecyl-2-methyl-sn-glycerol.

R¹ may further be a ceramide residue. Ceramides are endogenous lipophilic amides which are to be found in particular bound in the cerebral matter and in the myelin of the CNS and have the general formula (IV)

where R⁴ is a long-chain fatty acid residue, in particular a fatty acid residue having 12 to 28 C atoms, R⁵ is a long-chain alkyl radical, in particular an alkyl radical having 12 to 28 C atoms and R⁶ is H.

R¹ may further be a residue of a primary or secondary alcohol having 12 to 24 carbon atoms, in particular 13 to 22 carbon atoms, where the alcohols may be saturated or mono- or polyunsaturated.

R¹ may further be an acylglycerobenzyl ether residue, it being possible to employ such compounds in particular as starting materials for synthesizing lysophospholipids.

The residue R¹ may be present in the compounds of the invention in enantiopure form or as racemic mixture.

R² can be all the residues occurring in natural phospholipids and sphingomyelins. R² is in particular an ethanolamine residue, an N-methylethanolamine residue or a propanolamine residue, where the residues are provided where appropriate with suitable protective groups, for example BOC. R² may further be a choline residue. R² is preferably —CH₂—CH₂—N⁺(CH₃)₃. R² may further be a glycerol residue (—CH₂—CH(OH)—CH₂(OH)) and be an oligoglycerol, in particular a di- or triglycerol residue. Further suitable R² residues are glycoglycerols, and serine residues. The glycerol and serine residues may also where appropriate be provided with suitable protective groups.

R² is a radical selected from C₁-C₈-alkyl or C₁-C₈-alkenyl or may have one of the meanings indicated above for R². If R³ has one of the meanings indicated for R², it is possible to form highly biologically active structures which, as novel cationic lipids, have great importance. Such cationic lipids can be employed for example for gene transfection.

R³ may, however, also have only a temporary character, that is to say assume the function of a protective group which is detached again later. In this case, R³ is preferably methyl, ethyl, allyl or propyl.

The compounds of the invention are very stable between pH 3 and pH 8 and can be used in particular as liposome constituents.

The invention further relates to a process for preparing a compound according to formula (I), which is characterized in that a compound of the formula (II) is esterified with a compound of the formula (III) HO—R³.

The compounds are derived from phospholipids and are produced for example from

by esterification of the phosphoric diester with glycerol:

Cholesterol derivatives can also be obtained correspondingly

These compounds can be prepared in various embodiments. They may also comprise oligoglycerols, e.g. for example glyceroglycerol, diglyceroglycerol or triglyceroglycerol in place of glycerol. Diagrammatically, for example, cholesterol-phospho-monoglycerol-triglyceroglycerol has the following structural formula:

The compounds of the invention are particularly suitable for preparing liposomes and as liposome constituents. They confer particular properties on liposomes, e.g. long circulation times in the blood, targeted enrichment in the liver or else almost exclusive uptake in the spleen. It is also possible with the aid of the phosphoric triesters of the invention to form liposomes with novel properties, which have high serum stability, have long circulation times and accumulate exclusively in the spleen. Long circulation times are, however, also particularly important because the structures then do not, like known liposomes, accumulate in the liver but may hit other targets such as, for example, the spleen or, particularly importantly, be taken up by tumor cells. The compounds of the invention can therefore also be employed for the treatment of cancers.

The invention further relates to a novel synthetic route using the phosphoric triesters of the invention as intermediate. A particular advantage of the synthetic route of the invention is that the reaction direction (a) used in earlier syntheses is avoided, and according to (b) the important compound 1.2-dioleyl-sn-glycero-3-phosphoglycerol or corresponding compounds are liberated under neutral conditions:

R₁=1.2-dioleoyl-sn-glycerol

A substantial advantage of the novel management of the synthesis is the possibility of advancing apolar intermediates as far as possible in the synthesis, so that polar structures are introduced only at the end of the process. This is illustrated below in an example. Cardiolipins and analogous compounds are complicated structures which can be obtained only with great difficulty by synthesis in kg quantities. However, with the aid of our novel synthetic strategy, this is easily possible.

The synthesis is described for the example of R=palmitic acid. The starting material is 1.2-dipalmitoyl-sn-glycerol which is converted with phosphorus oxychloride in THF with triethylamine as base in the usual manner into 1.2-dipalmitoyl-sn-glycero-3-phosphoric dichloride:

Building Block I

The simple route for synthesizing cardiolipin, direct reaction with 2-benzylglycerol, unfortunately leads to predominant formation of the corresponding phospholane and is not practicable:

It is therefore necessary to use building block II, a protected glycerol derivative:

Building Block II

Linkage of building block I with building block II in THF with triethylamine then leads to building block III:

Building Block III

Building block III can then be reacted with building block I in the usual way to give the direct precursor of cardiolipin, which is then converted by

methanolysis into the dimethyl ester. The hydroxyl group on the middle glycerol is then liberated by catalytic hydrogenolysis. The methyl groups are removed by LiBr at neutral pH—the final product is cardiolipin.

The description is illustrated further by the following examples.

EXAMPLE 1

-   1) Cholesteryl-phospho-diglycerol C₃₃H₅₉O₈P (MW 614.801) -   2) Cholesteryl-phospho-glycerol-glyceroglycerol C₃₆H₆₅O₁₀P (MW     688.880) -   3) Cholesteryl-phospho-di-glycoglycerol C₃₇H₆₇O₁₀P (MW 702.907) -   4) 1.2-Dimyristoyl-sn-glycero-3-phospho-diglycerol C₃₇H₇₃O₁₂P (MW     740.953) -   5) 1.2-Dipalmitoyl-sn-glycero-3-phospho-diglycerol C₄₁H₈₁O₁₂P (MW     797.061) -   6) 1.2-Distearoyl-sn-glycero-3-phospho-diglycerol C₄₅H₈₉O₁₂P (MW     853.169) -   7) 1.2-Dioleoyl-sn-glycero-3-phospho-diglycerol C₄₅H₈₅O₁₂P (MW     849.137) -   8) 1.2-Dioleoyl-sn-glycero-3-phospho-di-glycoglycerol C₄₉H₉₃O₁₄P (MW     937.243) -   9) 1.2-Dioleoyl-sn-glycero-3-phospho-di-glyceroglycerol C₅₁H₉₇O₁₆P     (MW 997.295)

EXAMPLE 2

-   1) R₁: 1.2.-dimyristoyl-glycerol     -   R₂: choline     -   R₃: glycerol

and corresponding structures with 1.2.dioleoylglycerol.

-   2) R₁: 1.2-dioleoylglycerol     -   R₂: glycerol     -   R₃: methyl

EXAMPLE 3

Liposomes of the composition Molar ratio 1.2-Distearoyl-sn-glycero-3-phosphocholine 40% Cholesterol 30% Cholesterol-phospho-diglycerol 20% Cholesterol-phospho-glycerol, Na⁽⁺⁾ salt 10% 100%  accumulate predominantly in the spleen, whereas liposomes of the usual composition e.g. 1.2-Distearoyl-sn-glycero-3-phosphocholine 50% Cholesterol 40% 1.2-Distearoyl-sn-glycero-3-phosphoglycerol, Na⁽⁺⁾ 10% salt 100%  accumulate mainly in the liver. 

1. A compound of the formula (I)

in which R¹ is a residue selected from diacylglycerols, dialkylglycerols, acylalkyl-glycerols, and ceramides; R² and R³ are independently selected from glycerol or oligoglycerols.
 2. The compound of claim 1, characterized in that R³ is a glycerol residue.
 3. The compound of claim 1, wherein the compound is 1,2-dimyristoyl-sn-glycero-3-phospho-diglycerol.
 4. A process for preparing a compound according to formula (I) as claimed in claim 1, characterized in that a compound of the formula (II)

is esterified with a compound of the formula (III) HO—R³.
 5. A liposome comprising a compound as claimed in claim
 1. 6. A medicament comprising a compound as claimed in claim
 1. 7. A medicament comprising a liposome as claimed in claim
 5. 8. The compound of claim 1, wherein R1 is a diacylglycerol.
 9. The compound of claim 8, wherein the acyl groups of the diacylglycerol each independently comprise from 12 to 28 carbon atoms.
 10. The compound of claim 8, wherein the acyl groups of the diacylglycerol each are independently selected from mono-unsaturated and polyunsaturated radicals.
 11. The compound of claim 10, wherein the polyunsaturated radical is a di-unsaturated radical or a tri-unsaturated radical.
 12. The compound of claim 8, wherein the diacylglycerol comprises a fatty acid residue.
 13. The compound of claim 1, wherein the compound is 1,2-dipalmitoyl-sn-glycero-3-phospho-diglycerol.
 14. The compound of claim 1, wherein the compound is 1,2-distearoyl-sn-glycero-3-phospho-diglycerol.
 15. The compound of claim 1, wherein the compound is 1,2-dioleoyl-sn-glycero-3-phospho-diglycerol. 